The present invention relates to a method of controlling or regulating a brake.
A method of this type and a system is disclosed in German published patent application No. 195 26 645, for example. With this prior art method, data about the brake torque acting or the brake force acting and about at least one of the signals introduced into the actuator are sensed to determine the point of contact of the brake linings.
One disadvantage of the prior art method for determining the point of contact is, however, the use of expensive force sensors to determine the brake torques or brake forces. Further, it is known that force sensors have offset fluctuations and/or a zero point drift which are caused, for example, by aging, temperature effects, or overload.
Therefore, an object of the present invention is to provide a method of controlling or regulating which permits detecting and adjusting the clearance by employing parameters which are related to the actuator without requiring an information about the brake torque acting or the brake force acting. Another object of the present invention is to provide a controlling or regulating system for detecting and readjusting the clearance which operates independently of a special brake actuation and, in addition, permits readjusting the clearance also during travel of the automotive vehicle.
This object is achieved by the method of the present invention because to determine the contact making, the rigidity of the system on the side of the actuator is determined as a derivative of the actuator torque or the actuator force plotted against the actuator position.
More specifically, the idea of the present invention arranges for the actuator-side system rigidity to be monitored as to whether its value exceeds or falls below a threshold value.
The use of the quantity of system rigidity has the following advantages over the generic method:
a) The quantity xe2x80x98system rigidityxe2x80x99 can be used both in the initialisation phase (that is when newly adjusting the clearance after start-up of the vehicle, for example) and during actuation of the brake in a braking operation to determine the point of contact, it is also appropriate to readjust the clearance during each braking operation.
b) The analysis of the system rigidity does not require switching between the two operating modes of the power output unit, i.e. xe2x80x98speed-controlledxe2x80x99 and xe2x80x98torque-controlledxe2x80x99, because the excitation signal during the detection does not have to be a constant torque.
A controlling and regulating system for implementing the above-mentioned method is characterized in that
a) there is provision of a controller which can be switched between a first and a second control mode, and to which are sent, as input quantities, signals representative of a nominal value and an actual value of a force or a torque desired during actuation of the brake, a signal representative of the nominal actuator position, a contact signal representative of the contact making of the first friction surface on the second friction surface, as well as a switching variable, and the controller generating a first correcting variable,
b) there is provision of a clearance guiding and monitoring module to which are sent, as input quantities, a control variable for activating the clearance detection, and signals which correspond to the current being supplied to the actuator and to the actuator position, and which supplies the signal representative of the nominal actuator position, the switching variable, a second switching variable, and the contact signal, and generates a second correcting variable,
c) wherein the first correcting variable and the second correcting variable are sent to a selection circuit which, as a function of the second switching variable, sends one of the two correcting variables to an electronic activating circuit, whose output signal is used to drive the actuator.
The first control mode of the above-mentioned controller favorably corresponds to an actuator position control, while the second control mode corresponds to a brake force/brake torque control or a deceleration control.
According to another embodiment of the subject matter of the present invention, the clearance guiding and monitoring module includes a nominal value generator and a device for detecting the point of contact. The nominal value generator is furnished with the control variable, and the device for detecting the point of contact is furnished, as input quantities, with the signals which correspond to the current being supplied to the actuator and the actuator position, and wherein the nominal value generator generates the signal representative of the nominal actuator position, the first switching variable, the second switching variable and the second correcting variable, and the device for detecting the point of contact generates the signal representative of the contact making of the first friction surface on the second friction surface.
The device for detecting the point of contact preferably includes a first module for signal filtering and compensation of the inertia forces, a second module connected downstream of the first module for determining the actuator-side system rigidity, and a third module for comparing the system rigidity found with the threshold value. It is particularly appropriate when a fourth module is connected in parallel to the first, the second, and the third module for the allowability check, to which fourth module is sent, as an input quantity, the signal representative of the actuator position, and which generates a third switching variable which releases the function of the second and the third module.